Batteries are electrochemical energy storage devices that convert chemical energy intro electrical energy. One particular type of battery is a lithium-ion (Li-ion) battery. Lithium-ion batteries are desirable energy storage devices for portable electronics and electric and hybrid-electric vehicles, among other devices and systems, because they have a high specific energy compared to other electrochemical energy storage devices.
A key requirement for widespread adoption of battery technologies is providing a quick charging time, without hastening degradation of usable capacity. State of the art charging systems employ some variation of a constant-current constant-voltage (CCCV) charging procedure. In a CCCV charging procedure, a constant current is applied to the battery until a certain voltage is reached. Upon reaching the certain voltage, a constant voltage is applied until the charging current falls below a specified threshold, at which point the battery is considered fully charged. This charging procedure is very robust and simple to implement, however it also suffers from a fairly long charging time.
FIG. 1 illustrates a prior art CCCV charging procedure. Particularly, FIG. 1 includes a plot 102 which shows a battery voltage 104 over time, a plot 106 which shows a battery state of charge 108 over time, and a plot 110 which shows a battery current 112 over time. At a time t0, the CCCV charging procedure begins with a constant current (CC) phase in which a constant current of 6 amperes is applied to the battery. The constant current phase continues until the battery voltage reaches a voltage of 4.2 volts at a time t1. At the time t1, when the battery voltage reaches the voltage of 4.2 volts, the CCCV charging procedure switches to a constant voltage (CV) phase in which a constant voltage of 4.2 volts is applied to the battery. The constant voltage phase continues until the current reaches a very low threshold value (here set to 100 mA) at a time t2, at which point charging is defined to be complete. As shown, after the time t2, the charging current is set to zero.
As can be seen in FIG. 1, the battery state of charge 108 increases from 0% to about 75% during the constant current phase, which lasts about 22 minutes. However, during the constant voltage phase, the battery current 110 begins to decrease dramatically. As a result, the constant voltage phase takes about another 22 minutes in order to bring the battery state of charge 108 from 75% till end of charge. The constant voltage phase charges the battery at a substantially slower rate than the constant current phase, which greatly increases the amount of time to fully charge the battery.
Hence, it would be advantageous to provide a method for charging a lithium ion battery which reduces the length of time required to fully charge the battery while at the same time does not significantly accelerate ageing of the battery.